There is need for enabling electrical signals from a number of individual nerve fibers to be simultaneously received or for transmitting thereto signals that the nervous system can decode to produce natural responses, in both cases on a basis that provides a high degree of discreteness, on each of a number of data channels and on a basis that ensures stable operation over months or years with minimal risk to the patient.
As far as we are aware, the human nervous system has been connected to extra-corporeal devices only by gross electrodes placed on the surface of the skin, the brain or peripheral nerves or by microelectrodes placed in the brain or in various peripheral nerves.
Gross electrodes, since they provide a filtered and degraded signal from large masses of nervous or muscular tissue, lack both the discreteness necessary for the smooth and rapid control of multiple joints of a prosthetic limb or for sensory aids which can approach the detail of the natural sense organs. While microelectrodes provide such discreteness, they are very sensitive to movement and must be positioned by manipulators outside the body thereby not only limiting the number of microelectrodes that can be used but also presenting a risk of infection. They are not adapted for use over long periods of time and, additionally, they have high impedance thus requiring careful electrical shielding to prevent the loss of wanted signals in noise.